Before beginning a study of aircraft weighing procedure or attempting
the actual weighing of an aircraft, it is necessary to become familiar
with the weight and balance information in the applicable Aircraft Specification
or Type Certificate Data Sheet.

The specification for Taylorcraft, model BC and BCS airplanes, illustrated
in figure 3-6 has been reproduced in its entirety.
A few of the items need explaining; the rest are self-explanatory.

The designation 2 PCLM is read "2 place, closed land monoplane" and
indicates that the airplane seats two persons, has an enclosed cockpit,
can be operated from the solid part of the earth's surface, and has only
one wing. Two PCSM indicates that the airplane is a "2 place, closed sea
monoplane." It should be noted that the CG range, EWCG range, and the maximum
weight are different for the landplane and the seaplane. The location of
the seats indicates a side-by-side arrangement. The datum and the leveling
means are shown in the portion of the specification that is pertinent to
all models. Since the datum and the leveling means are directly connected
to weight and balance, they would be among the first items referred to
in planning the weighing operation. Figure 3-6. A
typical aircraft specification.

Although the location or arrangement of the landing gear is not shown
in figure 3-6, this information is given in the Aircraft
Specification or Type Certificate Data Sheets and the maintenance manual.
The location of the wheels has important significance, since this can be
used as a double check against actual measurements taken at the time of
weighing.

Weighing an Aircraft

Weighing an aircraft is a very important and exacting phase of aircraft
maintenance and must be carried out with accuracy and good workmanship.
Thoughtful preparation saves time and prevents mistakes.

If possible, aircraft should be weighed in a closed building where there
are no air currents to cause incorrect scale readings. An outside weighing
is permissible if wind and moisture are negligible.

Prepare Aircraft For Weighing

Drain the fuel system until the quantity indication reads zero, or empty,
with the aircraft in a level attitude. If any fuel is left in the tanks,
the aircraft will weigh more, and all later calculations for useful load
and balance will be affected. Only trapped or unusable fuel (residual fuel)
is considered part of the aircraft empty weight. Fuel tank caps should
be on the tanks or placed as close as possible to their correct locations,
so that the weight distribution will be correct.

In special cases, the aircraft may be weighed with the fuel tanks full,
provided a means of determining the exact weight of the fuel is available.
Consult the aircraft manufacturer's instructions to determine whether a
particular model aircraft should be weighed with full fuel or with the
fuel drained.

If possible, drain all engine oil from the oil tanks. The system should
be drained with all drain valves open. Under these conditions, the amount
of oil remaining in the oil tank, lines, and engine is termed residual
oil and is included in the empty weight. If impractical to drain, the oil
tanks should be completely filled.

The position of such items as spoilers, slats, flaps, and helicopter
rotor systems is an important factor when weighing an aircraft. Always
refer to the manufacturer's instructions for the proper position of these
items.

Unless otherwise noted in the Aircraft Specifications or manufacturer's
instructions, hydraulic reservoirs and systems should be filled; drinking
and washing water reservoirs and lavatory tanks should be drained; and
constant speed drive oil tanks should be filled.

Inspect the aircraft to see that all items included in the certificated
empty weight are installed in the proper location. Remove items that are
not regularly carried in flight. Also look in the baggage compartments
to make sure they are empty. Replace all inspection plates, oil and fuel
tank caps, junction box covers, cowling, doors, emergency exits, and other
parts that have been removed. All doors, windows, and sliding canopies
should be in their normal flight position. Remove excessive dirt, oil,
grease, and moisture from the aircraft.

Properly calibrate, zero, and use the weighing scales in accordance
with the manufacturer's instructions.

Some aircraft are not weighed with the wheels on the scales, but are
weighed with the scales placed either at the jacking points or at special
weighing points. Regardless of what provisions are made for placing the
aircraft on the scales or jacks, be careful to prevent it from falling
or rolling off, thereby damaging the aircraft and equipment. When weighing
an aircraft with the wheels placed on the scales, release the brakes to
reduce the possibility of incorrect readings caused by side loads on the
scales.

All aircraft have leveling points or lugs, and care must be taken to
level the aircraft, especially along the longitudinal axis. With light,
fixed wing airplanes, the lateral level is not as critical as it is with
heavier airplanes. However, a reasonable effort should be made to level
the light airplanes around the lateral axis. Accuracy in leveling all aircraft
longitudinally cannot be overemphasized.

Measurements

The distance from the datum to the main weighing point centerline, and
the distance from the main weighing point centerline to the tail (or nose)
weighing point centerline must be known to determine the CG relative to
the main weighing point and the datum.

An example of main weighing point to datum and main weighing point to
tail weighing point is shown in figure 3-7. See figure
3-8 for an example of main weighing point to datum
and main weighing point to nosewheel measurements.

These distances may be calculated using information from the Aircraft
Specifications or Type Certificate Data Sheets. However, it will often
be necessary to determine them by actual measurement.

After the aircraft has been placed on the scales (figure
3-9) and leveled, hang plumb bobs from the datum, the main weighing point,
and the tail or nose weighing point so that the points of the plumb bobs
touch the floor. Make a chalk mark on the floor at the points of contact.
If desired, a chalk line may be drawn connecting the chalk marks. This
will make a clear pattern of the

weighing point distances and their relation to the datum. Record the weights
indicated on each of the scales and make the necessary measurements while
the aircraft is still level.

After all weights and measurements are obtained and recorded, the aircraft
may be removed from the scales. Weigh the tare and deduct its weight from
the scale reading at each respective weighing point where tare is involved.

Balance Computation

To obtain gross weight and the CG location of the loaded airplane, first
determine the empty weight and the EWCG location. When these are known,
it is easy to compute the effect of fuel, crew, passengers, cargo, and
expendable weight as they are added. This is done by adding all the weights
and moments of these additional items and recalculating the CG for the
loaded airplane.

The scale readings and measurements recorded on the sample form in figure
3-10 form the basis for the examples of computing the empty weight
and the empty weight CG.

Empty Weight

The empty weight of the aircraft is determined by adding the net weight
on each weighing point. The net weight is the actual scale reading, less
the tare weight.

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This gives the aircraft weight as weighed.

Empty Weight CG

The CG location is found through the progressive use of two formulas.
First calculate the total moments using the following formulas:

Moment = Arm x Weight

then divide the sum of the moments by the total weights involved:

Consequently, the CG, as weighed, is 57.67 in from the datum.

Since the aircraft was weighed with the oil tank full, it is necessary
to remove the oil to obtain the empty weight and empty weight CG.

Again using the formula:

The EWCG is located 61.64 in aft of the datum.

The maximum allowable gross weight as shown in the Aircraft Specifications
is 1,733 pounds. By subtracting the aircraft empty weight from this figure,
the useful load is determined to be 450 pounds.